Polymeric compositions stabilized with esters of a thiofumaric acid



United States Patent 3,342,773 POLYMERIC COMPOSITIONS STABILIZED WITH ESTERS OF A THIOFUMARIC ACID Stanley B. Mirviss, Stamford, Conn., and Adam F.

Kopacki, Westwood, N.J., assignors to Staulier Chemical Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Sept. 18, 1964, Ser. No. 397,622 17 Claims. (Cl. 26045.85)

ABSTRACT OF THE DISCLOSURE Solid polymer compositions containing, in admixture, thiofumarate esters as ultra-violet light stabilizers. The solid polymers are hydrocarbon polymers, polyester polymers and vinyl polymers. The preferred thiofumarate ester is n-butyl dithiofumarate. The preferred amount of thiofumarate ester to be usedis 0.1 to 5.0% by weight based on the weight of the polymer.

This invention relates to the stabilization of polymeric materials against deterioration resulting from exposure to ultraviolet light and similar actinic radiation. The invention is particularly concerned with the stabilization of such materials by the inclusion therein of esters of a thiofumaric acid wherein one or both of the hydroxy oxygens have been replaced by sulfur.

It is well known that plastics and polymeric materials generally are suceptible to a characteristic type of photocatalyzed degradation when exposed to sunlight or other sources of ultraviolet rays. Although the effect varies with different materials, it commonly manifests itself initially as a weakening of the tensile strength of the polymer which on continued exposure becomes increasingly brittle until a point is reached at which mechanical failure occurs. Color changes often accompany the breakdown. In extreme instances the polymer may be transformed into a powdery mass.

There have been numerous proposals for producing plastics having increased durability in the presence of ultraviolet radiation. The most familiar of these proposals consists in blending the plastic or polymer with a material which in itself is a strong ultraviolet absorber. It is this latter property which apparently affords protection of the plastic from the damaging actinic radiation. In fact, it is customary to refer to the aforesaid additives as ultraviolet stabilizers. Because of their inherently poor resistance to ultraviolet light, the successful commercialization of synthetic polymers is tied in closely with the development of a suitable stabilizer.

Whereas the principal function of an ultraviolet stabilizer is that it provides protection of the polymer, certain ancillary features and characteristics are also necessary. It is, for instance, highly important that the stabilizer should not modify or cause adverse changes in the polymer. A particularly vexatious characteristic of many plastic additives is their tendency to impart color or stain to the polymer in which they are incorporated, ultraviolet stabilizers being especially prone to this type of behavior. Such side effects cannot be tolerated where a clear or colorless polymer is needed. Even pigmented or dyed plastic materials are deleteriously affected by stabilizer staining since it causes over-all color degradation. Other undesirable side effects often encountered are odor, toxicity production, softening, bleeding and the like. A desideratum from the commercial standpoint is that the stabilizer be readily available or economical to manufacture.

We have now discovered that excellent ultraviolet stabilizing of polymers can be achieved without encountering the aforesaid undersirable side effects by in- Patented Sept. 19, 1967 corporating in the polymer an ester of thiofumaric acid having the following formula:

propyl, etc., substituted phenyl wherein the substituents are lower alkyl, lower alkoxyl, chlorine, fluorine, bromine, etc, and cycloalkyl, e.g. cyclopentyl, cyclohexyl and the like and Z and Z represent oxygen or sulfur, it being un. derstood that one of Z and Z is always sulfur.

Exemplary compounds falling Within the ambit of the above depicted formula including the following:

methyl monothiofumarate ethyl dithiofumarate ethyl monot-hiofumarate n-butyl dithiofumarate isopentyl monothiofumarate isopentyl dithiofumarate n-hexyl dithiofumarate phenyl dithiofumarate diphenyl dithiofumara'te benzyl dithiofumarate n-octyl dithiofumarate tetradecyl dithiofumarate tetradecyl monothiofumarate cyclohexyl dithiofumarate a-napthyl dithiofumarate.

Esters of thiofumaric acid are in general known chemical entities, the description and preparation of which can be found in the technical and chemical literature as typified by such well known publications as Chemical Abstracts, the indices of which list numerous thiofumarate esters. For instance, a suitable procedure for preparing theiofumarate esters is described by Sumrell et al. in J.A.C.S., 18, 4313 (1954) in which fumaryl chloride is reacted with an organic mercaptan. As an illustration of the reaction, n-butyl thiofumarate was prepared in yield by reacting fumaryl chloride with n-butyl mercaptan while using an organic base such as pyridine to take up the hydrogen chloride by-product, Alternately, the reaction mixture can be refluxed until the hydrogen chloride is expelled in which case a neutralizing base is not required.

In practicing the invention, the thiofumarate ester can be blended or incorporated into the polymer by any of the conventional methods commonly used for mixing such materials with resins and plastics. A typical procedure comprises milling on heated rolls, although deposition from solvents and dry blending are other well known techniques.

In testing the stabilizers of the invention, we have found them singularly effective in protecting poly-u-olefins, diolefins, copolymers of olefins or olefins and diolefins and other hydrocarbon polymers, polymers of substituted vinyl compounds and polyesters against deterioration v not produce any undesirable side effects. Even after exposure periods in the neighborhood of 1,000 hours, test samples of polymers showed slight loss of mechanical strength while remaining substantially free of stain or coloration.

The polymers stabilized as contemplated herein can be cast, extruded, rolled or molded into sheets, rods, tubes, piping, filaments and other shaped articles, including sheets or films ranging from 0.5 to 100 mils in thickness. The polymer compositions of our invention can be applied as coatings to paper, cloth, wire, metal foil and are suitable for the manufacture of synthetic fibers and fabrics. Although the quantity of stabilizer is not particularly critical, it is recommended that the concentration based on the weight of the polymer be maintained in the neighborhood of 0.01 to about 5.0%.

The thiofurnarate esters as described herein are suitable for stabilizing a wide variety of solid polymer compositions against deterioration brought on by exposure to actinic radiation. In this connection mention is made of any of the normally solid polymers derived from the polymerization of a-mono-olefinic, aliphatic and arylsubstituted aliphatic hydrocarbons containing from two to ten carbon atoms. Typical poly-a-olefins include polyethylene, polypropylene, poly(3-methylbutene 1), poly(4- methylpentene-l), poly(pentene-1), poly(3,3-dimethylbutene-l poly(4,4-dimethylbutene-1), poly(octene-1 poly(decene-l), polystyrene and the like. Copolymers of such olefins as those prepared from ethylene and propylene or ethylene and the butenes or the like are also protected as are polydiolefins i.e. polybutadiene or polyisopropene and olefin-diolefin copolymers of the type as butadiene-styrene or isobutylene-isoprene copolymers. Polymeric materials prepared from olefins and/or diolefins containing some vinylic monomers such as acrylonitrile or vinyl chloride as illustrated by the so-called ABS resins, acrylonitrile, butadiene and styrene terpolymers, are considered to be within the scope of this invention as are polymers of substituted vinyl monomers such as vinyl chloride, vinylidene dichloride, vinyl acetate, acrylonitrile and the like. The aforelisted polymers and copolymers have been generically termed polymers of ethylenically unsaturated monomers in the prior art. Polyester resins with and without added styrene, divinylbenzene and the like are also stabilized by means of the thiofumarate esters.

We have ascertained that the stabilizers of the invention are particularly useful for preventing photo-degradation by ultraviolet light or sunlight of stereo-regular polyolefins such as isotactic polypropylene. Isotactic polypropylene is a stereo-regular polymer wherein the monomeric units are linked predominantly head to tail with the methyl groups on one side of the helical chain rather than the more common arrangement with methyl groups randomly distributed on both sides of the chain. Moreover, this isotactic or singular arrangement of substituents attached to the chain promotes an orderly alignment of the molecules. Such stereo-regular polymers often exhibit a high degree of crystallinity and are much superior in physical properties to attactic polymers having a random distribution of monomeric units. Stereoblock polymers wherein long segments of the chain are in one configuration or the other and also polymers with amorphous regions are also protected. For a fuller description of such polymers, reference is made to the Scientific American, 197 No. 3, pages 98-104 (1957); 205 No. 2, pages 33-41 (1961). Amorphous or appreciably amorphous polymers are also stabilized.

Although the molecular weight of polymers varies over wide limits, the stabilizer compounds of the invention are not restricted to any particular molecular weight range of polymer, and in fact it has been our finding that excellent protection can be realized with polymers having a broad or narrow range. Moreover, the so-called amorphous low molecular weight poly-a-olefin waxes or oils are likewise susceptible to stabilization by means of the compounds of the invention.

Polyesters which can be protected against ultraviolet radiation by means of thiofumarate esters are well known chemical entities and are described at length in the technical literature and numerous US. patents. One type of polyester is derived from the addition polymerization of ethylenically unsaturated organic esters, particularly vinyl ester monomers, and in this connection mention is made of acrylic esters, vinyl esters and in general any organic ester containing a la configuration wherein R", R R and R represent hydrogen or an organic hydrocarbyl substituent, The polymerization is commonly efi'ectuated by contacting the monomer with a polymerization initiator such as an organic peroxide with or without the application of heat Another type of-polyester which can be stabilized in accordance with the invention is formed by the successive esterification of dicarboxylic acids with polyglycols. The resulting polymeric ester consists of alternate linkages of the dicarboxylic acid and polyglycol residues produced by the elimination of water from between the reactants. The resulting polymers may be linear or cross-linked depending on the selection of the components. For instance, a glycol wherein the hydroxyl groups are terminally situated may produce a linear type of polyester with certain dibasic acids whereas such polyglycols as exemplified by glycerol give rise to a cross-linked polymer such as the well known Glyptals formed by reacting'glycerol with the dicarboxylic acid, phthalic acid, in the form of its anhydride.

Modifications of polyesters are the well known alkyd resins which are obtained by forming a polyester by reacting a polyglycol and an alpha-beta-ethylenically unsaturated dior polycarboxylic acid and cross-linking the residual ethylene double bonds with a suitable crosslinking agent.

In a more specific and detailed sense, the alkyd resins as above referred to having a plurality of polymerizable alpha-beta-ethylenically unsaturated linkages may be produced by combining together a polyhydric alcohol with a polycarboxylic acid or its anhydn'de which contains alphabeta-ethylenic unsaturation. It: is generally understood that the acid or its anhydride includes the designation polycarboxylic acid and such terminology will be understood in the description as herein set forth. Saturated carboxylic acids are also frequently included in the reaction mixture for the purpose of modifying the properties of the resin. From the standpoint of costs, the unsaturated polycarboxylic acids most commonly utilized are maleic, usually in the form of the anhydride, and fumaric acid. be employed are exemplified by citraconic, itaconic, aco- Other alpha-beta-unsaturated carboxylic acids which may be employed are exemplified by citraconic, itaconic, aconitic and mesaconic acids; The chemical andtechnical literature can be consulted for the names of other suitable acids. An acid often used for modifying the properties of a polyester resin is phthalic, acid, commonly in the form of its anhydride. Other such acids withbenzenoid or aromatic unsaturation which behave as saturated acids in that their benzenoid unsaturated structure does not enter into any common ethylenic type polymerization are commonly selected to produce various and particular properties and ofiects in the alkyd resin. Reference is made to such acids as isophthalic, adipic, azelaic, tetrachlorophthalic acid, sebacic, suberic, endomethylenetetrahydrophthalic and hexachloroendomethylenetetrahydrophthalic.

As illustrative of the polyhydric alcohols applicable for the synthesis of alkyd resins, mention is made of ethylene ture may be consulted for the names of the less common polyglycols. It should be pointed out that as with the dicarboxylic acid, a polyglycol alcohol may be selected which is ethylenically unsaturated and thereby giving residual ethylenic double bonds for the purpose of crosslinking the polyester'with concomitant modification in physical and chemical properties.

In preparing an alkyd resin, the polycarboxylic acid and appropriate polyhydric alcohol are commonly reacted at elevated temperatures in the presence of an inert atmosphere. The reaction is normally carried out at a temperature ranging from about 150 C. to about 230 C.; the inert atmosphere is conveniently provided by carbon dioxide or nitrogen gas. Generally, the total number of moles of alcohol exceeds the total number of moles of acid by about 5 to 20% since the latter figures are required to eifect complete esterification, although the proportions are not critical. A relatively inert organic solvent such as xylene is sometimes useful in carrying out the reaction. Since the reaction is an esterification, water is given off and should be removed from the system. After essentially all of the water has been expelled, any solvent is removed and after the mixture cools, the appropriate unsaturated monomeric cross-linking agent added. If cross-polymerization or linkage is to be prolonged, the presence of a suitable inhibitor is necessary.

Unsaturated monomers suitable for use as cross-linking agents can be selected from a wide variety of polymerizable compounds characterized by the presence of a CH =CH group. Examples of such monomers are styrene, vinyltoluene, methylacrylate, divinylbenzene, diallylphthalate, dimethylstyrene, methylmethacrylate, vinyl-acetate, butadiene, and the like. It is also a common practice to employ special monomers in order to secure particular effects. In this connection, mentioned is made of triallylcyanurate useful in imparting high heat resistance to resins, alkylallyldiglycolate for use as a refractive modifier, While diallylphenylphosphonate has been employed to impart fire resistance.

Three groups of components which we have found particularly suitable and convenient for preparing polyesters are: (1) acids such as maleic, fumaric, itaconic, phthalic and the like; (2) alcohols or glycols such as allyl alcohol, ethylene glycol and diethylene glycol; (3) unsaturated hydrocarbons such as styrene, cyclopentadiene and the like. For example, the polyesters disclosed in United States Patent No. 2,255,313 are illustrative of these unsaturated polyesters. Certain commercial polyesters such as the Laminacs also form satisfactory copolymers. Also polyesters such as generally described in United States Patent No. 2,443,736, containing an alkenyl aryl crosslinking agent, such as diallyl phthalate, and the reaction product of an alpha, beta ethylenically unsaturated polycarboxylic acid free of non-benzoid unsaturation, such as phthalic acid, and at least one glycol, such as ethylene glycol and/ or diethylene glycol may be used.

The amounts of the components useful in preparing polyesters may vary widely. In most instances, approximately two parts by weight of an unsaturated alkyd resin to one part by weight of the monomeric cross-linking agent is suitable although as above mentioned, the proportions may be varied over Wide limits.

Another important polymer which can be stabilized in accordance with the invention is polyvinylchloride. This polymer is commonly produced by the emulsion polymerization using a redox initiator for polymerizing vinyl chloride. One type of polyvinylchloride is the so-called rigid or unplasticized polyvinylchloride and this particular modification of polyvinylchloride can be effectively stabilized by the compounds of the invention. As has previously been pointed out elsewhere herein, the thiofumaric esters are effective as stabilizers either for the polymers themselves or various copolymers and terpolymers and mixtures thereof. One class of polymer compositions which lends itself to stabilization by means of the compounds of the invention is resin mixtures which are blends or copolymers of a plastic such as polystyrene or styreneacrylonitrile copolymer with a rubber usually a butadieneacrylonitrile copolymer. Such compositions may be intimate physical mixtures of the two components, the socalled polyblends or a true terpolymer, that is, an ABS resin, possibly produced by block or graft techniques. An example of the latter case is a graft copolymer of styrene on nitrile rubber. Typical compositions include 20-30% acrylonitrile, 2030% butadiene and 40-60% styrene. The abbreviation ABS is taken from the initial letters of the three monomers.

For a more detailed description of the various polymers, copolymers and terpolymers which are susceptible to stabilization in accordance with the invention, they are described at great length in the technical and chemical publications. In this connection, reference is made to such well-known treatises as Polyester Resins by J. R. Lawrence, Reinhold Publication Corp, New York (1960) and Textbook of Polymer Science by F. W. Billmeyer, published by Interscience Publishers, New York (1962).

The following examples illustrate the procedure for preparing stabilized polymer compositions of the invention although the inclusion of such examples is not to be taken as limiting or otherwise imposing any restriction on the invention, and it is to be understood that variations in practicing the same Without departing from the scope or spirit thereof will be apparent to those skilled in the art to which the said invention pertains.

EXAMPLE 1 A dry blend consisting of 0.5% by weight of n-butyl dithiofumarate and 50 g. of isotactic polypropylene was subjected to compression molding in the usual manner at a temperature of 400 F. for six minutes at 2000 psi. The blended polymer was compression molded or extruded into a 25 mil sheet and thereafter cut into square samples measuring 2 inches on the side. A like sample containing no stabilizer was also prepared and tested. The samples were then exposed in a xenon arc weatherometer operating at 6000 watts. The Water cycle was adjusted whereby each sample was subjected to 18 minutes of Water spray and 102 minutes of dry exposure for each two hours of exposure. Exposure damage to the samples of polypropylene was assessed with respect to change of structural strength.

Only after a period of exposure in excess of 982 hours, did the test sheet of polypropylene exhibit signs of brittleness in the flexure test. Nor was there any evidence at this time of any surface crazing or any coloration of staining. A blank specimen of unstabilized polypropylene which was exposed concurrently with thestabilized product failed the flexure test after 250 to 300 hours exposure time.

The weatherometer as used in compiling the data and tests described herein was a weathering device of the xenon arc type capable of developing 6000 watts.

The polypropylene resin as used in the above described example is an unstabilized general purpose, high molecular weight polypropylene of the isotactic or crystalline type. Typically, it has a melt index of 4 at 230 C. and a specific gravity of 0.905. The resin was purchased under the tradename Profax and further identified as number 6501, type P-02004 and is supplied in the form of natural flakes. We have also used other commercially available grades of unstabilized isotactic polypropylene resin and the results obtained in using the various grades and types of polypropylene Were in general agreement.

EXAMPLE 2 The procedure of Example 1 was repeated but substituting polyethylene in lieu of polypropylene. In general, the results paralleled those obtained in the first example.

EXAMPLE 3 The procedure of Example 1 was repeated except that 7 the polypropylene was replaced by polyvinylchloride. In general, the degree of stabilization was comparable to that obtained in the previous examples.

EXAMPLE 4 The following example describes the procedure for using the compounds of the invention to stabilize a polyester of the alkyd type.

0.25 g. of n-butyl thiofumarate was thoroughly mixed with 5.0 g. of styrene, followed by the addition of 0.5 g. of benzoyl peroxide. The thoroughly blended components were next combined with 95 g. of Laminac 4123, which is a styrene-modified, medium viscosity polyester resin. To effect curing of the Laminac 4123, the composition was placed between pyrex glass plates, the edges sealed and the sandwich heated in an upright position 80 C. for 30 minutes and finally one hour at 120 C. The cured sample was removed from the mold, and placed in the weatherometer for testing as described in Example 1. The degree of stabilization of the polymer was in line with the results obtained in the case of the first example.

We claim:

1. A solid polymer composition comprising, in admixture, a solid polymer selected from the class consisting of a polymer of an ethylenically unsaturated monomer and a polyester resin, and, as an ultra-violet stabilizer therefor, a stabilizing quantity of an organic ester of a triofumaric acid of the formula:

wherein R and R are members selected from the group consisting of alkyl groups of from 2-24 carbon atoms, aryl, and cycloalkyl, and Z and Z being selected from the group consisting of oxygen and sulfur, at least one of which is sulfur.

2. The composition according to claim 1 wherein the solid polymer is a poly-a-olefin.

3. The composition according to claim 1 wherein the solid polymer is a vinyl polymer.

4. The composition according to claim 1 wherein the solid polymer is a polydiolefin.

5. The composition according to claim 2 wherein the poly-a-olefin is polypropylene.

6. The composition according to claim 2 poly-a-olefin is polyethylene.

wherein the 7. The composition according to claim 3 wherein said vinyl polymer is polyvinylchloride.

8. The composition according to claim 1 wherein said solid polymer is formed by polymerizing two different mono olefins.

- The composition according to claim 1 wherein said polymer is formed by polymerizing a mono olefin and 10. The composition according to claim 3 wherein said solid polymer is formed by polymerizing a vinyl monomer and a mono olefin.

11. The composition according to claim 3 wherein said polymer is formed by polymerizing a vinyl monomer and a diolefin.

12. The composition according to claim 1 wherein said solid polymer is formed by the mixed polymerization of acrylonitrile, butadiene and styrene.

13. The composition according to claim 1 wherein the solid polymer is a polyester resin.

14. A solid polymer composition comprising, in admixture, polypropylene and as an ultra-violet light sta-.

bilizer therefor about 0.1 to about 5.0% n-butyl dithiofumarate, said percent being 'by weight based on the weight of the polymer.

15. A solid polymer composition comprising, in admixture, polyvinylchloride and as an ultra-violet light stabilizer therefor about 0.1 to about 5.0% n-butyl dithiofumarate, said percent being by weight based on the weight of the polymer.

16. A solid polymer composition comprising, in admixture, a terpolymer formed by the polymerization of a mixture of acrylonitrile, butadiene and styrene and as an ultra-violet light stabilizer for said terpolymer about 0.1 to about 5.0% n-butyl dithiofumarate, said percent being by weight based on the weight of the polyer.

17. A solid polymer composition comprising, in admixture, an alkyd polyester and as an ultra-violet light stabilizer therefor about 0.1 to about 5.0% n-butyl dithiofumarate, said percent being by weight based on the weight of the polymer.

References Cited UNITED STATES PATENTS 2,539,362 l/1951 Darby 260-306 2,792,380 5/ 1957 Slocombe 260-45.85 2,839,492 6/1958 Caldwell et a1 26045.85 3,060,154 10/1962 Ham et al 260-455 DONALD E. CZAJ A, Primary Examiner. LEON I. BERCOVITZ, Examiner. G. W. RAUCHFUSS, V. P. HOKE, Assistant Examiners. 

1. A SOLID POLYMER COMPOSITION COMPRISING IN ADMIXTURE, A SOLID POLYMER SELECTED FROM THE CLASS CONSISTING OF A POLYMER OF AN ETHYLENICALLY INSATURATED MONOMER AND A POLYSTER RESIN, AND, AS AN ULTRO-VIOLET STABILIZER THEREFOR, A STABILIZING QUANTITY OF AN ORGANIC ESTER OF A TRIOFUMARIC ACID OF THE FORMULA:
 12. THE COMPOSITION ACCORDING TO CLAIM 1 WHEREIN SAID SOLID POLYMER IS FORMED BY THE MIXED POLYMERIZATION OF ACRYLOMITRILE, BUTADIENE AND STYRENE. 